#!/usr/bin/env python3

"""
This tool is for checking the security hardening options of the Linux kernel.

SPDX-FileCopyrightText: Alexander Popov <alex.popov@linux.com>
SPDX-License-Identifier: GPL-3.0-only

This module performs input/output.
"""

# pylint: disable=missing-function-docstring,line-too-long,too-many-branches,too-many-statements

import os
import gzip
import sys
import tempfile
import subprocess
import shutil
from argparse import ArgumentParser
from typing import TextIO, Any
import re
import json
from .checks import add_kconfig_checks, add_cmdline_checks, normalize_cmdline_options, add_sysctl_checks
from .engine import StrOrNone, TupleOrNone, ChecklistObjType
from .engine import print_unknown_options, populate_with_data, perform_checks, override_expected_value


# The kernel-hardening-checker version format:
#   'major.linux_kernel_version.minor'
__version__ = '0.6.17.1'

SUPPORTED_ARCHS = ['X86_64', 'X86_32', 'ARM64', 'ARM', 'RISCV']


def mprint(mode: StrOrNone, *args: Any, **kwargs: Any) -> None:
    if mode != 'json':
        print(*args, **kwargs)


def _open(file: str) -> TextIO:
    try:
        if file.endswith('.gz'):
            return gzip.open(file, 'rt', encoding='utf-8')
        return open(file, encoding='utf-8')
    except FileNotFoundError:
        sys.exit(f'[-] ERROR: unable to open {file}, are you sure it exists?')
    except PermissionError:
        sys.exit(f'[-] ERROR: unable to open {file}, permission denied')


def get_local_kconfig_file(version_fname: str) -> tuple[StrOrNone, str]:
    kconfig_1 = '/proc/config.gz'
    if os.path.isfile(kconfig_1):
        return kconfig_1, 'OK'

    kconfig_2 = '/boot/config-'
    with _open(version_fname) as f:
        line = f.readline()
        assert(line), f'empty {version_fname}'
        assert(line.startswith('Linux version ')), f'unexpected contents of {version_fname}'
        parts = line.split()
        ver_str = parts[2]
        kconfig_2 = kconfig_2 + ver_str
    if os.path.isfile(kconfig_2):
        return kconfig_2, 'OK'

    return None, f'didn\'t find {kconfig_1} or {kconfig_2}'


def get_local_sysctl_file() -> tuple[StrOrNone, str]:
    sysctl_bin = shutil.which('sysctl')
    if not sysctl_bin:
        # fix for Debian
        if os.path.isfile('/sbin/sysctl'):
            sysctl_bin = '/sbin/sysctl'
    if not sysctl_bin:
        return None, 'sysctl command is not found on this machine'

    _, sysctl_tmpfile = tempfile.mkstemp(prefix='sysctl-')
    with open(sysctl_tmpfile, 'w', encoding='utf-8') as f:
        ret = subprocess.run([sysctl_bin, '-a'], check=False, stdout=f,
                             stderr=subprocess.STDOUT, shell=False).returncode
        if ret != 0:
            print(f'[!] WARNING: sysctl command returned {ret}')
        if os.stat(sysctl_tmpfile).st_size == 0:
            return None, f'sysctl command returned {ret}, stdout is empty'
    return sysctl_tmpfile, 'OK'


def detect_arch_by_kconfig(fname: str) -> tuple[StrOrNone, str]:
    arch = None

    with _open(fname) as f:
        for line in f.readlines():
            if m := re.match("CONFIG_([A-Z0-9_]+)=y$", line):
                option = m.group(1)
                if option not in SUPPORTED_ARCHS:
                    continue
                if arch is None:
                    arch = option
                else:
                    return None, 'detected more than one architecture in kconfig'

    if arch is None:
        return None, 'failed to detect architecture in kconfig'
    return arch, 'OK'


def detect_arch_by_sysctl(fname: str) -> tuple[StrOrNone, str]:
    arch_mapping = {
        'ARM64': r'^aarch64|armv8',
        'ARM': r'^armv[3-7]',
        'RISCV': r'^riscv32|riscv64',
        'X86_32': r'^i[3-6]?86',
        'X86_64': r'^x86_64'
    }
    with _open(fname) as f:
        for line in f.readlines():
            if line.startswith('kernel.arch'):
                value = line.split('=', 1)[1].strip()
                for arch, pattern in arch_mapping.items():
                    assert(arch in SUPPORTED_ARCHS), 'invalid arch mapping in sysctl'
                    if re.match(pattern, value):
                        return arch, value
                return None, f'{value} is an unsupported arch'
        return None, 'failed to detect architecture in sysctl'


def detect_kernel_version(fname: str) -> tuple[TupleOrNone, str]:
    with _open(fname) as f:
        ver_pattern = re.compile(r"^# Linux/.+ Kernel Configuration$|^Linux version .+")
        for line in f.readlines():
            if ver_pattern.match(line):
                line = line.strip()
                parts = line.split()
                ver_str = parts[2].replace('+', '-')
                ver_numbers_str = ver_str.split('-', 1)[0]
                ver_numbers = ver_numbers_str.split('.')
                if len(ver_numbers) >= 3:
                    if all(map(lambda x: x.isdecimal(), ver_numbers)):
                        return tuple(map(int, ver_numbers)), 'OK'
                msg = f'failed to parse the version "{parts[2]}"'
                return None, msg
        return None, 'no kernel version detected'


def detect_compiler(fname: str) -> tuple[StrOrNone, str]:
    gcc_version = None
    clang_version = None
    with _open(fname) as f:
        for line in f.readlines():
            if line.startswith('CONFIG_GCC_VERSION='):
                gcc_version = line[19:-1]
            if line.startswith('CONFIG_CLANG_VERSION='):
                clang_version = line[21:-1]
    if gcc_version is None or clang_version is None:
        return None, 'no CONFIG_GCC_VERSION or CONFIG_CLANG_VERSION'
    if gcc_version == '0' and clang_version != '0':
        return f'CLANG {clang_version}', 'OK'
    if gcc_version != '0' and clang_version == '0':
        return f'GCC {gcc_version}', 'OK'
    sys.exit(f'[-] ERROR: invalid GCC_VERSION and CLANG_VERSION: {gcc_version} {clang_version}')


def print_checklist(mode: StrOrNone, checklist: list[ChecklistObjType], with_results: bool) -> None:
    if mode == 'json':
        output = []
        for opt in checklist:
            output.append(opt.json_dump(with_results))
        print(json.dumps(output))
        return

    # table header
    sep_line_len = 91
    if with_results:
        sep_line_len += 30
    print('=' * sep_line_len)
    print(f'{"option_name":^38}|{"type":^7}|{"reason":^18}|{"decision":^10}|{"desired_val":^12}', end='')
    if with_results:
        print('| check_result', end='')
    print()
    print('=' * sep_line_len)

    # table contents
    ok_count = 0
    fail_count = 0
    for opt in checklist:
        if with_results:
            assert(opt.result), f'unexpected empty result of {opt.name} check'
            if opt.result.startswith('OK'):
                ok_count += 1
                if mode == 'show_fail':
                    continue
            else:
                assert(opt.result.startswith('FAIL')), \
                       f'unexpected result "{opt.result}" of {opt.name} check'
                fail_count += 1
                if mode == 'show_ok':
                    continue
        opt.table_print(mode, with_results)
        print()
        if mode == 'verbose':
            print('-' * sep_line_len)
    print()

    # final score
    if with_results:
        fail_suppressed = ''
        ok_suppressed = ''
        if mode == 'show_ok':
            fail_suppressed = ' (suppressed in output)'
        if mode == 'show_fail':
            ok_suppressed = ' (suppressed in output)'
        print(f'[+] Config check is finished: \'OK\' - {ok_count}{ok_suppressed} / \'FAIL\' - {fail_count}{fail_suppressed}')


def parse_kconfig_file(_mode: StrOrNone, parsed_options: dict[str, str], fname: str) -> None:
    with _open(fname) as f:
        opt_is_on = re.compile(r"CONFIG_[a-zA-Z0-9_]+=.*$")
        opt_is_off = re.compile(r"# CONFIG_[a-zA-Z0-9_]+ is not set$")

        for line in f.readlines():
            line = line.strip()
            option = None
            value = None

            if opt_is_on.match(line):
                option, value = line.split('=', 1)
                if value == 'is not set':
                    sys.exit(f'[-] ERROR: bad enabled Kconfig option "{line}"')
                if value == '':
                    print(f'[!] WARNING: found strange Kconfig option {option} with empty value')
            elif opt_is_off.match(line):
                option, value = line[2:].split(' ', 1)
                assert(value == 'is not set'), \
                       f'unexpected value of disabled Kconfig option "{line}"'
            elif line != '' and not line.startswith('#'):
                sys.exit(f'[-] ERROR: unexpected line in Kconfig file: "{line}"')

            if option in parsed_options:
                sys.exit(f'[-] ERROR: Kconfig option "{line}" is found multiple times')

            if option:
                assert(value is not None), f'unexpected None value for {option}'
                parsed_options[option] = value


def parse_cmdline_file(mode: StrOrNone, parsed_options: dict[str, str], fname: str) -> None:
    with _open(fname) as f:
        line = f.readline()
        if not line:
            sys.exit(f'[-] ERROR: empty cmdline file "{fname}"')

        opts = line.split()

        line = f.readline()
        if line:
            sys.exit(f'[-] ERROR: more than one line in "{fname}"')

        for opt in opts:
            if '=' in opt:
                name, value = opt.split('=', 1)
            else:
                name = opt
                value = '' # '' is not None
            if name in parsed_options and mode != 'json':
                print(f'[!] WARNING: cmdline option "{name}" is found multiple times')
            value = normalize_cmdline_options(name, value)
            assert(value is not None), f'unexpected None value for {name}'
            parsed_options[name] = value


def parse_sysctl_file(mode: StrOrNone, parsed_options: dict[str, str], fname: str) -> None:
    with _open(fname) as f:
        if os.stat(fname).st_size == 0:
            sys.exit(f'[-] ERROR: empty sysctl file "{fname}"')

        sysctl_pattern = re.compile(r"[a-zA-Z0-9/*._-]+ ?=.*$")
        sysctl_eperm_pattern = re.compile(r"sysctl: permission denied on key '([a-zA-Z0-9/*._-]+)'")
        for line in f.readlines():
            line = line.strip()
            if not line or line.startswith('#'):
                continue
            if line.startswith('sysctl: '):
                # this line came from stderr
                if m := sysctl_eperm_pattern.match(line):
                    option = m.group(1)
                    parsed_options[option] = 'permission denied'
                continue
            if not sysctl_pattern.match(line):
                sys.exit(f'[-] ERROR: unexpected line in sysctl file: "{line}"')
            option, value = line.split('=', 1)
            option = option.strip()
            value = value.strip()
            # sysctl options may be found multiple times, let's save the last value:
            parsed_options[option] = value

    # let's check the presence of some ancient sysctl option
    # to ensure that we are parsing the output of "sudo sysctl -a > file"
    if 'kernel.printk' not in parsed_options and mode != 'json':
        print(f'[!] WARNING: ancient sysctl options are not found in {fname}, try checking the output of "sudo sysctl -a"')

    # let's check the presence of a sysctl option available for root
    if 'kernel.cad_pid' not in parsed_options and mode != 'json':
        print(f'[!] WARNING: sysctl options available for root are not found in {fname}, try checking the output of "sudo sysctl -a"')

    # also warn about an explicit "permission denied" error for sysctl options available for root
    if 'permission denied' in parsed_options.values() and mode != 'json':
        print('[!] WARNING: got "permission denied" for some of sysctl options, try checking the output of "sudo sysctl -a" manually')


def refine_check(mode: StrOrNone, checklist: list[ChecklistObjType], parsed_options: dict[str, str],
                 target: str, source: str) -> None:
    source_val = parsed_options.get(source, None)
    if source_val:
        override_expected_value(checklist, target, source_val)
    else:
        # remove the target check to avoid false results
        mprint(mode, f'[!] WARNING: can\'t check {target} without {source}')
        checklist[:] = [o for o in checklist if o.name != target]


def perform_checking(mode: StrOrNone, version: TupleOrNone,
                     kconfig: StrOrNone, cmdline: StrOrNone, sysctl: StrOrNone) -> None:
    config_checklist = [] # type: list[ChecklistObjType]
    arch = None

    # detect the kernel architecture
    if kconfig:
        arch, msg = detect_arch_by_kconfig(kconfig)
        if arch is None:
            sys.exit(f'[-] ERROR: {msg}')
        mprint(mode, f'[+] Detected architecture: {arch}')
    else:
        assert(not cmdline), 'wrong perform_checking() usage'
        assert(sysctl), 'wrong perform_checking() usage'
        arch, msg = detect_arch_by_sysctl(sysctl)
        if arch is None:
            mprint(mode, f'[!] WARNING: {msg}, arch-dependent checks will be dropped')
        else:
            mprint(mode, f'[+] Detected architecture: {arch} ({msg})')

    if kconfig:
        # kconfig allows to determine the compiler for building the kernel
        compiler, msg = detect_compiler(kconfig)
        if compiler:
            mprint(mode, f'[+] Detected compiler: {compiler}')
        else:
            mprint(mode, f'[!] WARNING: can\'t detect the compiler: {msg}')

    if kconfig:
        # add relevant Kconfig checks to the checklist
        assert(arch), 'arch is mandatory for the kconfig checks'
        add_kconfig_checks(config_checklist, arch)

    if cmdline:
        # add relevant cmdline checks to the checklist
        assert(arch), 'arch is mandatory for the cmdline checks'
        add_cmdline_checks(config_checklist, arch)

    if sysctl:
        # add relevant sysctl checks to the checklist
        add_sysctl_checks(config_checklist, arch)

    if version:
        # populate the checklist with the kernel version data
        populate_with_data(config_checklist, version, 'version')

    parsed_kconfig_options = {} # type: dict[str, str]
    if kconfig:
        # populate the checklist with the parsed Kconfig data
        parse_kconfig_file(mode, parsed_kconfig_options, kconfig)
        populate_with_data(config_checklist, parsed_kconfig_options, 'kconfig')
        # refine the values of some checks
        refine_check(mode, config_checklist, parsed_kconfig_options,
                     'CONFIG_ARCH_MMAP_RND_BITS', 'CONFIG_ARCH_MMAP_RND_BITS_MAX')
        refine_check(mode, config_checklist, parsed_kconfig_options,
                     'CONFIG_ARCH_MMAP_RND_COMPAT_BITS', 'CONFIG_ARCH_MMAP_RND_COMPAT_BITS_MAX')
        # and don't forget to skip these Kconfig checks in --generate

    if cmdline:
        # populate the checklist with the parsed cmdline data
        parsed_cmdline_options = {} # type: dict[str, str]
        parse_cmdline_file(mode, parsed_cmdline_options, cmdline)
        populate_with_data(config_checklist, parsed_cmdline_options, 'cmdline')

    if sysctl:
        # populate the checklist with the parsed sysctl data
        parsed_sysctl_options = {} # type: dict[str, str]
        parse_sysctl_file(mode, parsed_sysctl_options, sysctl)
        populate_with_data(config_checklist, parsed_sysctl_options, 'sysctl')
        # refine the values of some checks
        refine_check(mode, config_checklist, parsed_kconfig_options,
                     'vm.mmap_rnd_bits', 'CONFIG_ARCH_MMAP_RND_BITS_MAX')
        refine_check(mode, config_checklist, parsed_kconfig_options,
                     'vm.mmap_rnd_compat_bits', 'CONFIG_ARCH_MMAP_RND_COMPAT_BITS_MAX')

    # now everything is ready, perform the checks
    perform_checks(config_checklist)

    if mode == 'verbose':
        # print the parsed options without the checks (for debugging)
        if kconfig:
            print_unknown_options(config_checklist, parsed_kconfig_options, 'kconfig')
        if cmdline:
            print_unknown_options(config_checklist, parsed_cmdline_options, 'cmdline')
        if sysctl:
            print_unknown_options(config_checklist, parsed_sysctl_options, 'sysctl')

    # finally print the results
    print_checklist(mode, config_checklist, True)


def main() -> None:
    # Report modes:
    #   * verbose mode for
    #     - reporting about unknown kernel options in the Kconfig
    #     - verbose printing of ComplexOptCheck items
    #   * json mode for printing the results in JSON format
    output_modes = ['verbose', 'json', 'show_ok', 'show_fail']
    parser = ArgumentParser(prog='kernel-hardening-checker',
                            description='A tool for checking the security hardening options of the Linux kernel')
    parser.add_argument('--version', action='version', version=f'%(prog)s {__version__}')
    parser.add_argument('-m', '--mode', choices=output_modes,
                        help='select a special output mode instead of the default one')
    parser.add_argument('-a', '--autodetect', action='store_true',
                        help='autodetect and check the security hardening options of the running kernel')
    parser.add_argument('-c', '--config',
                        help='check the security hardening options in a Kconfig file (also supports *.gz files)')
    parser.add_argument('-v', '--kernel-version',
                        help='extract the kernel version from a version file (such as /proc/version) instead of using a Kconfig file')
    parser.add_argument('-l', '--cmdline',
                        help='check the security hardening options in a kernel command line file (such as /proc/cmdline)')
    parser.add_argument('-s', '--sysctl',
                        help='check the security hardening options in a sysctl output file (the result of "sudo sysctl -a > file")')
    parser.add_argument('-p', '--print', choices=SUPPORTED_ARCHS,
                        help='print security hardening recommendations for the selected architecture')
    parser.add_argument('-g', '--generate', choices=SUPPORTED_ARCHS,
                        help='generate a Kconfig fragment containing the security hardening options for the selected architecture')
    args = parser.parse_args()

    mode = None
    if args.mode:
        mode = args.mode
        mprint(mode, f'[+] Special report mode: {mode}')

    if args.autodetect:
        if args.config or args.kernel_version or args.cmdline or args.sysctl:
            sys.exit('[-] ERROR: --autodetect should find the configuration, no other arguments are needed')
        if args.print:
            sys.exit('[-] ERROR: --autodetect and --print can\'t be used together')
        if args.generate:
            sys.exit('[-] ERROR: --autodetect and --generate can\'t be used together')

        mprint(mode, '[+] Going to autodetect and check the security hardening options of the running kernel')

        version_file = '/proc/version'
        kernel_version, msg = detect_kernel_version(version_file)
        if kernel_version is None:
            sys.exit(f'[-] ERROR: parsing {version_file} failed: {msg}')
        mprint(mode, f'[+] Detected version of the running kernel: {kernel_version}')

        kconfig_file, msg = get_local_kconfig_file(version_file)
        if kconfig_file is None:
            sys.exit(f'[-] ERROR: detecting kconfig file failed: {msg}')
        mprint(mode, f'[+] Detected kconfig file of the running kernel: {kconfig_file}')

        cmdline_file = '/proc/cmdline'
        if not os.path.isfile(cmdline_file):
            sys.exit(f'[-] ERROR: no kernel cmdline file {cmdline_file}')
        mprint(mode, f'[+] Detected cmdline parameters of the running kernel: {cmdline_file}')

        sysctl_file, msg = get_local_sysctl_file()
        if sysctl_file is None:
            sys.exit(f'[-] ERROR: failed to get sysctls: {msg}')
        mprint(mode, f'[+] Saved sysctls to a temporary file {sysctl_file}')

        perform_checking(mode, kernel_version, kconfig_file, cmdline_file, sysctl_file)

        os.remove(sysctl_file)
        sys.exit(0)

    if args.config:
        mprint(mode, f'[+] Kconfig file to check: {args.config}')
    if args.cmdline:
        mprint(mode, f'[+] Kernel cmdline file to check: {args.cmdline}')
    if args.sysctl:
        mprint(mode, f'[+] Sysctl output file to check: {args.sysctl}')

    if args.config:
        assert(not args.autodetect), 'unexpected args'
        if args.print:
            sys.exit('[-] ERROR: --config and --print can\'t be used together')
        if args.generate:
            sys.exit('[-] ERROR: --config and --generate can\'t be used together')

        if args.kernel_version:
            kernel_version, msg = detect_kernel_version(args.kernel_version)
        else:
            kernel_version, msg = detect_kernel_version(args.config)
        if kernel_version is None:
            if args.kernel_version is None:
                print('[!] HINT: you can provide the kernel version file through --kernel-version option')
            sys.exit(f'[-] ERROR: {msg}')
        mprint(mode, f'[+] Detected kernel version: {kernel_version}')

        perform_checking(mode, kernel_version, args.config, args.cmdline, args.sysctl)
        sys.exit(0)
    elif args.cmdline:
        sys.exit('[-] ERROR: checking cmdline depends on checking Kconfig')
    elif args.sysctl:
        # separate sysctl checking (without kconfig)
        assert(not args.autodetect), 'unexpected args'
        if args.kernel_version:
            sys.exit('[-] ERROR: --kernel-version is not needed for --sysctl')
        if args.print:
            sys.exit('[-] ERROR: --sysctl and --print can\'t be used together')
        if args.generate:
            sys.exit('[-] ERROR: --sysctl and --generate can\'t be used together')
        perform_checking(mode, None, None, None, args.sysctl)
        sys.exit(0)

    if args.print:
        assert(not args.autodetect and
               args.config is None and
               args.cmdline is None and
               args.sysctl is None), \
               'unexpected args'
        if args.kernel_version:
            sys.exit('[-] ERROR: --kernel-version is not needed for --print')
        if args.generate:
            sys.exit('[-] ERROR: --print and --generate can\'t be used together')
        if mode and mode not in ('verbose', 'json'):
            sys.exit(f'[-] ERROR: wrong mode "{mode}" for --print')
        arch = args.print
        assert(arch), 'unexpected empty arch from ArgumentParser'
        config_checklist = [] # type: list[ChecklistObjType]
        add_kconfig_checks(config_checklist, arch)
        add_cmdline_checks(config_checklist, arch)
        add_sysctl_checks(config_checklist, arch)
        mprint(mode, f'[+] Printing kernel security hardening options for {arch}...')
        print_checklist(mode, config_checklist, False)
        sys.exit(0)

    if args.generate:
        assert(not args.autodetect and
               args.config is None and
               args.cmdline is None and
               args.sysctl is None and
               args.print is None), \
               'unexpected args'
        if mode:
            sys.exit(f'[-] ERROR: wrong mode "{mode}" for --generate')
        if args.kernel_version:
            sys.exit('[-] ERROR: --kernel-version is not needed for --generate')
        arch = args.generate
        config_checklist = []
        add_kconfig_checks(config_checklist, arch)
        print(f'CONFIG_{arch}=y') # the Kconfig fragment should describe the architecture
        for opt in config_checklist:
            if opt.name in ('CONFIG_ARCH_MMAP_RND_BITS', 'CONFIG_ARCH_MMAP_RND_COMPAT_BITS', 'CONFIG_LSM'):
                continue # don't add Kconfig options with a value that needs refinement
            if opt.expected == 'is not off':
                continue # don't add Kconfig options without explicitly recommended values
            if opt.expected == 'is not set':
                print(f'# {opt.name} is not set')
            else:
                print(f'{opt.name}={opt.expected}')
        sys.exit(0)

    parser.print_help()
    sys.exit(0)
